add package to local mirror

[gobo7]

i have my own local (as in-house only) 14.04 mirror. the other day i
was testing the most recent release of chromium and had problems. i
found out that i could not back out the changes as the version that
had been running was absent from the mirror. (i plan on upgrading
the drives so i can turn off cleaning; a project for a different day.)

i located the packages and i can see where they should exist in the
file structure. what i don't understand is how the mirror keeps
track of packages and how to reinsert deleted packages.

so what steps can/should i take to manually reinsert packages into
my mirror?

thanks,
gobo